The present invention relates generally to optical disk recording apparatus based on a mark-length recording scheme which irradiates a laser light beam onto a recording surface of an optical disk to form pits therein for desired information recording. More particularly, the present invention relates an improved optical disk recording apparatus which provides for improved reproductive characteristics, such as less jitter, less deviations from predetermined pit or land lengths and a lower error rate, of signals recorded on cyanine-based and phthalocyanine-based optical disks at various recording speeds.
Among various known standards for writable optical disks is the CD-WO (CD Write Once) standard that is commonly known as the xe2x80x9cOrange Bookxe2x80x9d. According to a recording strategy based on this CD-WO standard or Orange Book, a laser-light irradiation time for forming pits (i.e., recording-laser-power irradiation time) is set to the following length, for both the standard and double recording speeds, irrespective of which kind of dye material is used in the recording layer of the optical disk:
(nxe2x88x921)T+xcex943T
where xe2x80x9cnTxe2x80x9d represents a length of a pit to be formed with xe2x80x9cnxe2x80x9d being a variable in the range of 3-11, and xe2x80x9cxcex943Txe2x80x9d is an extra laser power value for addition to recording of a shortest 3T pit.
In this CD-WO standard, a target pit depth parameter xcex2 is also defined for a target pit depth of a pit to be formed. Specifically, this target pit depth parameter xcex2 is defined as a ratio between positive (plus-side) and negative (minus-side) peak values A1 and A2 of a signal (high frequency or HF signal) read out from the optical disk and having its d.c. component removed therefrom, as represented by
xcex2=(A1+A2)/(A1xe2x88x92A2)
At a same recording speed, the target pit depth parameter xcex2 becomes greater in value as the recording power increases but becomes smaller as the recording power decreases. Further, to keep the target pit depth parameter xcex2 constant in a situation where the recording speed is varied, it is necessary to increase the recording laser power as the recording speed is increased. According to the Orange Book standard, the target pit depth parameter xcex2 is prescribed to be fixed between 0% and 8% for every selected recording speed; that is, a particular recording laser power level is set depending on each selected recording speed so that the value of the target pit depth parameter xcex2 always falls between 0% and 8% irrespective of the selected recording speed.
Further, in Japanese Patent Application No. HEI-8-233596 filed by the same assignee of the instant application, there is disclosed a recording strategy in accordance with which the laser-light irradiation time is set to a length of
(nxe2x88x92K)T+xcex1(nT)xe2x88x92xcex2(mT)
, where xe2x80x9cKxe2x80x9d is a constant,
xcex1(nT) represents a modification amount per pit length xe2x80x94for example, a relationship of xcex1(3T)xe2x89xa7xcex1(4T)xe2x89xa7xcex1(5T)xe2x89xa7. . . xe2x89xa7xcex1(8T) and hence (xcex1(3T) greater than xcex1(8T)) may be appliedxe2x80x94, and
xcex2(mT) represents a modification amount per immediately preceding land length which is a parameter unrelated to the target pit depth parameter xcex1xe2x80x94at least, a relationship of xcex2 (3T)xe2x89xa7xcex2(4T)xe2x89xa7xcex2(5T)xe2x89xa7. . . xe2x89xa7xcex2(8T) and hence (xcex2(3T) greater than xcex2(8T)) maybe appliedxe2x80x94. In this case, the constant K is set to be between 0T and 0.5T for a six-times recording speed and between 0T and 0.3T for an eight-times recording speed, regardless of the kind of dye material used in the optical disk""s recording layer.
However, the recorded conditions of the optical disk would considerable vary depending on the selected dye material and recording speed, so that the standardized laser-irradiation time control based on the Orange Book could not achieve optimum reproductive characteristics of the recorded signals. Further, with the target pit depth parameter xcex2 fixed between 0% and 8% irrespective of the variably selected recording speed as noted above, the reproduced signals would become more likely to have an unwanted waveform distortion as the recording speed is increased, which would substantially deteriorate the reproductive characteristics of the signals. Further, for some types of disks, the recording strategy disclosed in Japanese Patent Application No. HEI-8-239396 could not necessarily attain optimum reproductive characteristics of the recorded signals.
It is therefore an object of the present invention to provide an optical disk recording apparatus which can record signals on an optical disk in such a way that optimum reproductive characteristics of the recorded signals are always achieved for any kinds of dye material used in the disk""s recording layer and for any selected recording speeds.
In order to accomplish the above-mentioned object, the present invention provides an optical disk recording device which, in accordance with a length of a pit to be recorded, a laser power irradiation time is controlled to take a length of (nxe2x88x92K)T+xcex943T, where nT represents the length of a pit to be formed, K is a constant and xcex943T represents an extra laser power value for addition to recording of a 3T pit. The control section also performs control for imparting an additional top power pulse to an initial part of each pit-forming laser power irradiation so as to increase the laser power level over a standard recording power level temporarily for a predetermined time period. The K and xcex943T values and the level of the additional top power pulse are optimized in the present invention in accordance with a combination of the disk type and the recording speed. This arrangement always achieves optimum reproductive characteristics of signals recorded on cyanine-based and phthalocyanine-based optical disks at any recording speeds.
Further, the present invention provides an optical disk recording apparatus capable of recording on both a cyanine-based optical disk and a phthalocyanine-based optical disk at a variably selected recording speed, which comprises a control section that controls a recording laser power level in such a manner that a target pit depth parameter, related to a target value of a pit depth to be formed in the optical disk, is made smaller in value as the recording speed is increased. With this arrangement, even signals recorded at a relatively high recording speed can be reproduced with improved reproductive characteristics with the possibility of an unwanted waveform distortion effectively minimized.
Recording on the optical disk while controlling the recording laser power level in such a manner that the target pit depth parameter is made smaller in value as the recording speed is increased may be realized in the following manner. Namely, optimum target pit depth parameter values, which become smaller in value as the recording speed is increased, are determined previously, and the thus-determined optimum target pit depth value for each of the recording speeds is prestored into memory as a target pit depth value. Then, after selection of a desired recording speed, trial recording is performed under the optimum power control (OPC) as prescribed by the Orange Book standard, so that a recording laser power level achieving the target pit depth value predetermined for the selected recording speed is automatically determined and prestored into memory as a target recording laser power value. Actual recording on the optical disk can be carried out at that selected recording speed while controlling the actual recording laser power level in accordance with the prestored target recording laser power value.
In a similar manner to the conventional counterpart, the OPC control in this instance automatically performs a series of operations of: carrying out trial recording on the power calibration area (PCA) located inwardly of the lead-in area of the optical disk while variously changing the recording laser power level with the recording speed kept constant; reproducing the thus-recorded signal; removing a d.c. component from the reproduced high-frequency (HF) signal by means of a high-pass filter; detecting positive (plus-side) and negative (minus-side) peak values of the reproduced signal; calculating a ratio between a sum and a difference between these two peak values to thereby determine a target pit depth for each of the recording laser power levels; comparing the calculated target pit depth to a target pit depth value preset for that recording speed so as to find a particular recording laser power level capable of achieving a calculated target pit depth closest to the preset target pit depth value; and storing the particular recording laser power level as a target recording laser power value.
As another approach for recording on the optical disk while controlling the recording laser power level in such a manner that the target pit depth parameter is made smaller in value as the recording speed is increased, the following operations may be carried out. Namely, in stead of the optical disk recording apparatus itself performing the OPC control, a recording laser power level achieving an optimum target pit depth value, which is made smaller in value as the recording speed is increased, is determined previously for each disk type (such as for each dye material used in the disk""s recording layer, disk manufacturer, etc.) and prestored into memory of the optical disk recording apparatus. Then, in recording, the optical disk recording apparatus identifies the type of the optical disk installed therein from, for example, a disk ID registered in the disk and reads out a particular one of the prestored recording laser power levels in accordance with the identified disk type and selected recording speed, to thereby carry out the actual recording while controlling the actual recording laser power level in accordance with the read-out prestored recording laser power level.